chore: bump @progress/wct-a11y-spec from 2.17.0 to 2.18.0 in /src-a11y

Bumps [@progress/wct-a11y-spec](https://github.com/telerik/web-components-ux) from 2.17.0 to 2.18.0.
- [Commits](https://github.com/telerik/web-components-ux/commits)

---
updated-dependencies:
- dependency-name: "@progress/wct-a11y-spec"
  dependency-version: 2.18.0
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

Signed-off-by: dependabot[bot] <[email protected]>

Author: dependabot[bot]